Active Acoustic Enhancement

Performing arts venues are primarily designed with specific acoustic considerations in mind to ensure optimal sound quality for a given range of performances.

The implementation of variable acoustics systems allows performing arts venues to adapt to a wide range of performance types.

Variable acoustics can be achieved through passive methods (e.g., rotating panels and/or curtains) or active electro-acoustic systems.

To enhance its cultural repertoire and function as a genuine multi-purpose venue, a performance hall necessitates adaptable acoustics.

Different performance types require distinct acoustic conditions. The design of these spaces must be flexible. This need for flexibility has led to a growing demand for multi-purpose halls that can accommodate a variety of performance types, including orchestral music, chamber music, theater, conferences, live music, or orchestral performance with choir and vocal accompaniment and as well as solo recitals.

When a sound is emitted into a room, the sound waves travel through space and are repeatedly reflected at the room boundaries resulting in acoustic reverberation.

Active Acoustic Enhancement refers to a range of technologies and systems designed to improve or modify the acoustics of a performance space by using electronic means. Unlike traditional passive acoustic treatments, which involve physical alterations to the space (such as the addition of absorptive panels, diffusers, or architectural features), active acoustic enhancement systems use microphones, loudspeakers, and digital signal processing to dynamically alter the acoustic properties.

Throughout the history of active acoustic systems, there have been many different approaches to shaping the acoustics, which can be categorized as follows: in-line, regenerative, and hybrid.

HOLOPHONIX aims to give users the ability to select and combine all these techniques in one tool.

In-line systems use directional microphones placed near the sources to pick up direct sound and loudspeakers distributed throughout the venue. Reverberation is generated either by algorithmic methods (such as feedback delay networks) or by convolution with impulse responses, captured in mono, stereo, multichannel or Ambisonics formats. Due to the directional characteristics and the spatial separation of microphones and loudspeakers, the loop gain is very low and feedback is avoided.

The regenerative approach uses signal loops between microphones and loudspeakers to create reverberation. The basic idea is that the picked up signals are fed back through the loudspeakers with different delays, but a reverberation stage can be added to the signal chain for more flexibility. Regenerative systems produce a very natural result, but rely largely on the nature and tone of the existing room acoustics, leaving limited freedom to change the character of the acoustics.

A combination of both approaches is typically referred to as a hybrid system.

HOLOPHONIX aims to be the only solution on the market that combines the best active acoustics principles (in-line, regenerative, and hybrid) in a unique solution that offers total flexibility. All of these techniques can be used and combined with each other as required. This makes HOLOPHONIX the first ever Active Acoustic Enhancement solution based on a combination of different and complementary technologies.

The convolution and regenerative engines are expected to be available in 2025.

HOLOPHONIX is built around a multichannel algorithmic reverberation engine.

The generated room effect consists of four temporal segments : the direct sound, a few early reflections generated by a delay line with multiple tap delays, a set of dense late reflections (referred to as cluster) generated by multiple delay lines feeding a decorrelation matrix, and a late reverb tail synthesized by a Feedback Delay Network (FDN)

This reverb topology has been integrated into HOLOPHONIX years ago and offers advanced possibilities for creating and tuning an artificial reverb.

Parametric reverberators (such as FDNs) are scalable and they allow for a continuous tuning of the time and frequency behavior of the room response

Feedback Delay Networks (FDNs) are recursive filters widely used for artificial reverberation and decorrelation. The FDN consists of N delay lines combined with attenuation filters fed back through a scalar feedback matrix.

The above animation is copyrighted by Prof. Sebastian J. Schlecht.

A convolution-based approach ensures an authentic and natural listening experience by preserving the acoustic signature of existing rooms.

A user can thus capture the impulse responses (IR) of any physical location (such as churches, symphony halls, or theaters) and process audio as though it were being played at that location.

This convolution engine allows a new level of realism and immersion.

The HOLOPHONIX convolution reverb engine will be the only solution available on the market capable of processing monophonic, stereophonic, and multi-channel impulse responses, up to 64 channels (equivalent to seventh-order Ambisonics) providing exceptional spatial accuracy and adding many more degrees of freedom.

Note that convolution processors are often difficult to parameterize. Control over the reverberation effect is generally limited to a few low-level parameters. Also, the CPU cost of such engines depends on the length of the processed IR.

The regenerative approach is probably the purest reverb engine, adding reflections back into the room based on its original reflections, thereby extending and preserving the room's unique ambience.

This method uses multiple microphones and loudspeakers across various channels to enhance the sound of the room by introducing more reflections from the boundaries than would occur naturally.

It is mainly based on signal loops between microphones and loudspeakers to generate reverberation.

The HOLOPHONIX Hybrid Reverb Engine offers a hybrid approach, combining a convolution reverb for recreating the early reflections of a measured impulse response (IR) with a feedback delay network (FDN) for synthesizing the reverberation tail.

As a result, the hybridization approach benefits both from the authenticity of the convolution technique and the flexibility of FDN-based renderer.

Our various reverberation technologies offer the ability to transform a performance hall with naturally dry acoustics into a versatile venue capable of hosting a wide range of events, from theatre productions to symphonic concerts.

These cutting-edge technologies give you total control over the acoustics of your venue, creating the perfect environment for both intimate performances, large classical ensembles, or amplified events. HOLOPHONIX goes beyond simple audio enhancement. It ensures the optimal acoustic experience for your entire space.

Thanks to the HOLOPHONIX interface and its 3D venue visualization, you can seamlessly switch between optimal acoustic settings for live music, orchestras, or speeches in just seconds.

With over than 40 years of experience in research on sound spatialization for artistic creation, the Institute for Research and Coordination in Acoustics/Music (Ircam) is one of the largest public research centers in the world dedicated to both musical expression and scientific research.

HOLOPHONIX, Amadeus, and Ircam have embarked on an ambitious development program aimed to develop the very first solution on the market that combines the best active acoustics principles (in-line, regenerative, and hybrid) in a unique solution that offers total flexibility.

Famous musical director and conductor Raphaël Pichon made a special request to HOLOPHONIX and Amadeus to design and implement an innovative system combining active acoustics and sound spatialization to maximize the audience experience.

A unique tailor-made sound system was designed and installed within the Théâtre de l'Archevêché - as part of the world-renowned Aix-en-Provence Festival - to subtly modify the acoustic characteristics of the theatre space using 35 microphones and more than 50 loudspeakers processed through HOLOPHOPNIX.

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The reverberation time of the theater is smaller than in other places designed for lyrical art, and it varies according to the zones — including rear seats, balcony, and under-balcony. Our approach was to homogenize the acoustic sound coming from the orchestra pit with the sound of the choir and the singers on stage, to make them coherent in timbre, volume level, and reverberated field.

Clément Vallon

Engineer | HOLOPHONIX